Dash temp gauge randomly drops

So this one has me a little stumped. Just when I get the car running great this happens :(. Basically the water temp gauge randomly drops to 0, and then it'll go back up to 90, then randomly go back to 0. There doesn't seem to be a patern just completely random. Sometimes it won't do it at, all other times it'll do it like 5 times in a 20min trip. It doesn't seem to affect how the car runs, wideband shows afrs are the same as usual so I'm thinking it's just the signal that goes to the dash is getting interrupted. I have checked the wiring to the cts and it looks like fine. Has anybody had a coolant temp sensor fail like this or could it be my instrument cluster is dying??

Could be the water pump impeller - sounds like classic symptoms of one that's dying/ broken, or coolant temp sensor. How long since you replaced it last?

Water pump was done when I rebuilt the engine about 4k ago, metal impeller too so that should be fine. Thermostat replaced at same time also. Cts is maybe 18 months old, so wouldn't expect it to go bad already, stranger things have happened though. Might order one and see if that's the problem?

I just replaced my Coolant Temp Sensor which was giving me dodgy readings - car was running rough and over-fueling

If the temperature is suddenly dropping to zero, it is more than likely to be a faulty temperature sensor. If it were anything else, the temperature drop would be a lot more gradual.

One other thing is the wiring. A fault there (like a break in the conductor) would also give similar symptoms.

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Originally Posted by wai

If the temperature is suddenly dropping to zero, it is more than likely to be a faulty temperature sensor. If it were anything else, the temperature drop would be a lot more gradual.

One other thing is the wiring. A fault there (like a break in the conductor) would also give similar symptoms.

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Yeah that's my thinking. Like the needle won't move around, it just goes bam, straight to zero then after like 2mins it shoots straight back up to 90. I guess I'll change the sensor and see what happens. But it's definitely not the cluster going right??

Is the temp sensor which signals ECU used to drive the dash gauge also, or is there another one ?
I know its a cheap pars but go check the electrical connector also.

Have a look in the electrical connector for the temp sensor as well. Sometimes the female terminals might need a little tweaking for a snug contact. You may also notice some blue corrosion on them as well.

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Originally Posted by Lito

But it's definitely not the cluster going right??

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Well, it could be, but check the others out first as they are a lot cheaper. Somewhere there is an intermittent signal coming through.